Blanks for forming moisture resistant containers are well known in the art. Score lines divide the blank into a plurality of panels. The container is formed by folding the blank along the score lines and appropriately sealing the edges. The blank usually comprises paperboard or fiberboard which is treated with a variety of waxes or polymeric substances to maintain the integrity of the carton. Toward this end, metal foils have also been used in laminate blank structures.
However, leakage through the material and seepage past an edge still remain as significant problems. A standard method of overcoming the leakage is to employ thicker sealant layers or polymeric sealants on the paperboard in the areas of the score line. U.S. Pat. No. 4,586,643 to Halabisky et al discloses use of polyethylene to minimize leakage when used in the horizontal score lines of the carton.
Other prior art sealing techniques include the hot melt application method of McNair, Jr. et al, in U.S. Pat. No. 3,365,111. The Brownlee et al U.S. Pat. Nos. 3,913,825 and 3,913,826 disclose use of a continuous thermoplastic band along the bottom edge of the blank which, when heated, melts and seals the edge of the bottom closure together when the container is formed.
Specific attempts to overcome the liquid seepage problem are seen in U.S. Pat. No. 3,305,383 to Gordy which teaches the method of impregnating a flat carton blank in certain confined areas with normally solid hydrophobic materials such as various waxes. The substrate is then heated to facilitate penetration of the hydrophobic material into the blank. U.S. Pat. No. 3,107,586 to Ragan teaches a method of preventing liquid seepage from paperboard containers which utilizes a hot melt or similar adhesive coated on certain of the overlapping portions of a carton while simultaneously applying a release agent material to the surface of the carton engaged by the overlapping portions.
With all of the attempts in the prior art to prevent such seepage, some leakage of material at the edge of overlapping areas still remains. Most of the prior art efforts to prevent liquid seepage have entailed using an adhesive along the edges to be sealed. Although such methods have decreased the amount of liquid seepage from the container, it is virtually impossible to coat the panel edges uniformly, and the results heretofore obtained have been less than satisfactory. Moreover, such processes mandate an additional step in carton production, and thus increase the overall cost of production.
It would be advantageous to have a means of mechanically preventing seepage of liquid from along the edges of sealed panels which would be fully compatible with existing production methods and which would not involve an additional production step.